Coated article resistant to corrosion with nano-crystalline layer

ABSTRACT

In some examples, an article including a substrate and a multi-layered coating on at least a portion of the substrate. The multi-layered coating including at least one nano-crystalline layer comprising a metal or a metal alloy and a corrosion resistant layer on the at least one nano-crystalline layer. The nano-crystalline layer defining an average grain size of less than 50 nanometers (nm) and the corrosion resistant layer including at least one of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.

This application claims the benefit of U.S. Provisional Application No. 62/490,286 filed Apr. 26, 2017, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to techniques for forming a nano-crystalline coating on articles, for example, for use in aerospace componentry, and articles including a nano-crystalline coating.

BACKGROUND

Aerospace components are often operated in relatively extreme environments that may expose the components to a variety of stresses and environmental factors. In some examples, the exposure of the components to corrosive environments may induce or accelerate erosion or degradation of the components leading to early fatigue or failure. In some examples, aerospace components have been developed that exhibit higher strength and durability using high density metals or metal alloys. However, some high-density metals or metal alloys may be relatively heavy, difficult to manufacture, or expensive making their use non-ideal for aerospace applications.

SUMMARY

In some examples, the disclosure describes an article including a substrate and a multi-layered coating on at least a portion of the substrate. The multi-layered coating including at least one nano-crystalline layer comprising a metal or a metal alloy and a corrosion resistant layer on the at least one nano-crystalline layer. The at least one nano-crystalline layer defining an average grain size of less than 50 nanometers (nm) and the corrosion resistant layer including at least one of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.

In some examples, the disclosure describes a method of forming an article including depositing at least one nano-crystalline layer on a substrate, the at least one nano-crystalline layer including a metal or a metal alloy and defines an average grain size of less than 50 nanometers (nm). The method also includes depositing a corrosion resistant layer on the at least one nano-crystalline layer, wherein the corrosion resistant layer includes at least one of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.

In some examples, the disclosure describes an article including a substrate, and a multi-layered coating applied on at least a portion of the substrate, the multi-layered coating including a first nano-crystalline layer comprising a metal or a metal alloy and a second nano-crystalline layer comprising cobalt or cobalt alloy on the first nano-crystalline layer. The first and second nano-crystalline layers each defining an average grain size of less than 50 nanometers (nm). The multi-layered coating also includes a corrosion resistant layer deposited on the second nano-crystalline layer, wherein the corrosion resistant layer includes a component selected from the list consisting of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic perspective view of an example article that includes a multi-layer coating applied to a least a portion of substrate.

FIG. 1B is a cross-sectional view of the article of FIG. 1A along line A-A.

FIG. 1C is a close-up, cross-sectional view of a section of the article of FIG. 1B, illustrating the construction of the multi-layer coating, which includes a nano-crystalline layer on the substrate and a corrosion resistant layer on the nano-crystalline layer.

FIG. 2 is a schematic cross-sectional view of another example article including a multilayer coating.

FIG. 3 is a flow diagram illustrating an example technique for forming an article including a multi-layer coating as described herein.

FIGS. 4A and 4B are photographs of the articles of Comparative Example 1 after a salt spray test.

FIG. 5 is photograph of the article Example 1 after a salt spray test.

DETAILED DESCRIPTION

In general, the disclosure describes articles and techniques for making articles that include a substrate having a nano-crystalline metal or metal alloy coating on at least a portion of the substrate. The techniques described herein may be used to form articles having a nano-crystalline layer that defines an ultra-fine-grain crystalline microstructure with an average grain size less than about 20 nanometers (nm). The nano-crystalline layer may be deposited as a relatively thin layer (e.g., about 0.05 mm to about 0.7 mm) that includes a metal or a metal alloy material. In some examples, the relatively thin nano-crystalline layer may exhibit improved strength and reduced weight characteristics compared to conventional titanium, steel, or other high-density metal components. Additionally, or alternatively, the metal or the metal alloy nano-crystalline layer may exhibit one or more of improved strength, durability, and corrosion resistance compared to alternative, non-nano-crystalline coatings of the same or similar composition. The nano-crystalline layer described herein may include layers comprising one or more metals particularly suited for applications needing high strength or durability.

In some examples, the nano-crystalline layer may include at least one nano-crystalline layer of cobalt metal or an alloy that includes cobalt metal. The cobalt may increase the strength of the nano-crystalline layer as well as impart some degree of corrosion protection to the underlying substrate compared to traditional materials used for aerospace components. However, the exposure of a nano-crystalline layer that includes cobalt to aqueous corrosive environments (e.g., the aqueous environments associated with operation of aerospace components) has surprisingly been found to cause the layer to become discolored having a dull, reddish-brown appearance. In accordance with examples described herein, an article may additionally include a corrosion resistant layer on the nano-crystalline layer configured to reduce the corrosion associated with aqueous corrosive environments (e.g., reduce or substantially prevent the corrosion and/or oxidation of the nano-crystalline layer). In some examples, the corrosion resistant layer may include nickel metal; a nickel alloy such as a nickel-phosphorus alloy, a nickel-sulfur alloy, a nickel-boron alloy, a nickel cadmium alloy, or a nickel-zinc alloy; cadmium metal; tin; or a tin alloy, such as a tin-zinc alloy. The deposition of such corrosion resistant layers on the nano-crystalline layer have been found to inhibit the discoloration of the nano-crystalline layer after exposure to an aqueous corrosive environment.

FIG. 1A is a schematic perspective view of an example article 10 that includes a multi-layer coating 14 applied to a least a portion of substrate 12. FIG. 1A includes a cutout section 16 that reveals substrate 12. FIG. 1B is a cross-sectional view of article 10 of FIG. 1A along line A-A, and FIG. 1C shows a close-up, cross-sectional view of article 10 at section 20 of FIG. 1B, illustrating the multi-layer construction of coating 14, which includes at least one nano-crystalline layer 22 on substrate 12 and corrosion resistant layer 24 on nano-crystalline layer 22.

As shown in FIG. 1A, in some examples, article 10 may be in the form of an aerospace component such as an airfoil (e.g., blade or vane) for a gas turbine engine. However, article 10 may include any one of a number of articles such as aerospace components that may benefit from the described strength characteristics, reduced weight, or corrosion resistant properties described herein. In some examples, article 10 may represent a different aerospace component including, for example, a housing, a bracket, an air duct, a manifold, a tube, a chevron ventilation outlet, a vane box plume tab, a variable vane actuator arm, a nose cone, a transition duct seal, an actuation ring, a flap, a casing, a frame, an accessory gear, a drive shaft, a rotor, a disc, a panel, a tanks, a cover, a flow surface, a turbine engine component, and the like. In some examples, article 10 may exhibit a complex three-dimensional geometry such as a turbine engine blade or vane as shown. In other examples, article 10 may be in the form of a sheet or a shaped-sheet component, such as an air flow surface or a housing component.

Substrate 12 of article 10 may include any suitable underlying substrate material(s) including for example, metal, metal alloy, polymeric material, composite material, or the like. In some examples, due to the improved strength properties imparted by nano-crystalline layer 22, underlying substrate 12 may be formed using relatively light weight or soft materials compared to other relatively dense or heavy components, such as titanium or steel. While the strength of nano-crystalline layer 22 may permit forming the substrate using relatively light weight components without significantly reducing the strength of the resultant component, it will be understood from the disclosure that the features and benefits obtained from the construction of multi-layer coating 14 may also be obtained using heavier materials for substrate 12. The description of substrate 12 is not intended to limit substrate 12 to a specific construction or selection of materials unless otherwise indicated.

In some examples, substrate 12 may include one or more relatively lightweight composite or polymeric materials. Suitable polymeric materials may include, for example, polyether ether ketone (PEEK), polyamide (PA), polyimide (PI), bis-maleimide (BMI), epoxy, phenolic polymers (e.g., polystyrene), polyesters, polyurethanes, silicone rubbers, copolymers, polymeric blends, and the like. Examples of composite materials may include reinforced polymeric materials. In some such examples, the reinforcement material may include, for example, fibrous material such as ceramic fibers, carbon fibers, or polymeric fibers; carbon nano-tubes; and the like. The presence of reinforcement materials in the polymeric material may increase the relative strength of the resultant substrate 12 compared to a substrate 12 that includes only polymeric material. In some examples, substrate 12 may include between about 10% to about 40% reinforcement materials (e.g., carbon fibers) mixed with one or more polymeric materials. Substrate 12 may also include one or more optional additives including, for example, binders, hardeners, plasticizers, antioxidants, and the like.

Substrate 12 may be formed using any suitable technique and have any suitable three-dimensional structure. For example, when forming substrate 12 using a polymeric material, substrate 12 may be formed using a molding process in which molten polymeric materials are combined with any optional additives or reinforcement materials and cast into a three-dimensional mold to form substrate 12 with the desired shape (e.g., a gas turbine airfoil). In some examples, the polymeric material may be injected into a mold containing reinforcement fibers, and the polymeric material may encase and solidify around the reinforcement fibers to form substrate 12 with the desired shape. In other examples, substrate 12 may be fabricated as a sheet, which may be substantially planar (e.g., planar or nearly planar) or sculpted into a desired shape (e.g., a panel in the shape of the leading edge of an airfoil) through subsequent processing.

In some examples, substrate 12 may include a structured substrate having a macro-porous structure that defines a plurality of pores. For example, substrate 12 may be a macro-porous material (e.g., a material that includes a plurality of pores, voided spaces, cavities, or the like (collectively referred to as “pores”)) that defines pores with an average size between about 75 micrometers (μm) and about 500 μm. For example, structured substrate 12 may include a foam material (e.g., metal-based foam substrate), a lattice structure, a truss structure, or similar complex three-dimensional structure that includes a plurality of pores.

In some such examples, at least some of the pores within a structured substrate 12 may be interconnected. The interconnectivity of the pores may produce multiple pathways within structured substrate 12 that may extend substantially across the thickness of substrate 12 (e.g., pathways that extend between different surfaces of structured substrate 12). In some examples, the pathways created by the pores may be used for dissipating heat by allowing a cooling liquid or gas to be circulated through the internal pathways of structured substrate 12. In other examples, at least some of the pores may be only partially interconnected or non-interconnected. At least some surfaces of the pores of substrate 12 (e.g., interior portions of structured substrate 12) may receive one or more of nano-crystalline layers 22 described further below. Additionally, or alternatively, at least some of the pores of structured substrate 12 may be at least partially filled with a polymeric material prior to the application of nano-crystalline layer 22. In some such examples, the polymeric material may be used to improve the smoothness of the exterior surfaces of substrate 12, impart vibrational dampening features to substrate 12, or both.

Article 10 includes multi-layer coating 14 applied to at least a portion of substrate 12. Multi-layer coating 14 includes at least one nano-crystalline layer 22 that includes a metal or a metal alloy that defines an ultra-fine-grain microstructure with an average grain size less than about 50 nanometers (nm) (e.g., less than 20 nm or less than 5 nm grain size). In some examples, the grain size of nano-crystalline layer 22 may increase the relative tensile strength of the resultant layer as well as the overall hardness of the layer, such that nano-crystalline layer 22 may be significantly stronger and more durable compared to a conventional metallic coating (e.g., coarser grain coating) of the same composition and thickness. In some examples, the increased strength and hardness of nano-crystalline layer 22 may allow for the layer to remain relatively thin (e.g., between about 0.025 millimeters (mm) and about 0.15 mm) without reducing the desired strength and hardness characteristics of the layer. Additionally, or alternatively, depositing nano-crystalline layer 22 on a lightweight substrate 12 material may help reduce the overall weight of article 10 by reducing the amount (e.g., volume) of denser materials that are traditionally used to form article 10. The combination of the relatively light weight material of substrate 12 and nano-crystalline layer 22 may result in a relatively high strength, relatively low weight article for aerospace components and other articles where weight and strength are relevant considerations.

Nano-crystalline layer 22 may include one or more ultra-fine-grain metal or metal alloy layers. Any suitable metals or metal alloys may be used in forming nano-crystalline layer 22 including, for example, cobalt, nickel, copper, iron, cobalt-based alloys, nickel-based alloys, nickel-cobalt alloys, copper-based alloys, iron-based alloys, or the like. In some examples, nano-crystalline layer 22 may consist essentially of the metal or the metal alloy, such that nano-crystalline layer 22 comprises at least 95 weight percent (wt. %) of the ultra-fine-grain metal or metal alloy in crystalline form. In some such examples, nano-crystalline layer 22 may consist essentially of nano-crystalline microstructure that each define a grain sizes of less than 50 nm or less than 20 nm. For example, nano-crystalline layer 22 may be an entirely nano-crystalline layer of ultra-fine-grain metal or metal alloy apart from trace impurities within the crystalline structure.

In some examples, nano-crystalline layer 22 may include at least one layer of cobalt or a metal alloy that includes cobalt (e.g., a nickel-cobalt alloy). Nano-crystalline cobalt has been found to impart improved strength and some degree of corrosion protection to article 10 compared to other more traditional materials used for aerospace components.

In some examples, nano-crystalline layer 22 may include a nickel-cobalt alloy, e.g., a layer of cobalt metal and nickel metal as an alloy that defines an ultra-fine-grain microstructure. The addition of nickel may improve the overall durability of nano-crystalline layer 22 and/or article 10 to resist impact damage from foreign objects during operation. For example, to improve impact damage resistance against foreign objects, traditional aerospace components have been formed or coated with thick layers of high strength metals such as titanium. Such techniques, however, may suffer from increased costs associated with processing and raw materials. Additionally, components formed from high strength metals such as titanium tend to result in relatively dense and heavy components which may be less desirable in applications where weight is an important consideration, such as aerospace applications. Forming article 10 to include a lightweight substrate 12 and a nickel-cobalt alloy as at least one nano-crystalline layer 22 may significantly reduce the weight of article 10 compared to those formed with traditional high strength metals (e.g., titanium) while also obtaining comparable or even improved durability and corrosion resistance properties from the alloyed nickel and cobalt metals.

In some examples, the overall thickness 18 of nano-crystalline layer 22 may be between about 0.025 mm (e.g., about 0.001 inches) and about 0.7 mm (e.g., about 0.028 inches), measured in a direction substantially normal to the surface of substrate 12 on which nano-crystalline layer 22 is applied. In some examples, thickness 18 of nano-crystalline layer 22 may be about 0.05 mm to about 0.15 mm (e.g., about 0.002 inches to about 0.006 inches). Additionally, or alternatively, thickness 18 of nano-crystalline layer 22 may be selectively varied on different portions of substrate 12 to impart various mechanical, barrier, or thermal properties to different sections of article 10. For example, in areas where increased impact damage resistance is desired, e.g., the leading edge of a turbine blade, the relative thickness of nano-crystalline layer 22 may be increased to impart greater strength in that region. Additionally, or alternatively, thickness 18 of nano-crystalline layer 22 may be reduced in regions where increased impact damage resistance is less desired, or nano-crystalline layer 22 may be omitted from article 10 in those regions.

Nano-crystalline layer 22 may be deposited on substrate 12 using any suitable plating technique including, for example, one or more electro-deposition techniques, to form a coated metallic layer of a desired thickness and nano-crystalline grain structure. For example, substrate 12 may be suspended in suitable electrolyte solution that includes the selected metal or metal alloy used to form nano-crystalline layer 22. A pulsed or direct current (DC) may then be applied to substrate 12 to plate the substrate with the metal or the metal alloy. In some examples, the duration of the pulsed current may be selected to obtain an ultra-fine-grain metal or metal alloy nano-crystalline layer 22 exhibiting an average grain size less than about 50 nm, less than about 20 nm, or less than about 5 nm.

In some examples, substrate 12 may be initially metallized in select locations with a base layer (e.g., base layer 34 of FIG. 2) of metal to aid or facilitate the deposition of nano-crystalline layer 22 on substrate 12 using electro-deposition. For example, in some implementations in which substrate 12 includes polymeric materials, a metallized base layer 34 such as copper, nickel, or cobalt may be deposed on substrate 12 using electroless deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), cold spraying, gas condensation, or the like to establish a metal layer on the polymer substrate, which in turn may promote the subsequent formation via electro deposition and/or adhesion of nano-crystalline layer 22 to article 10. In some examples, the metalized base layer may include one or more of the metals used to form nano-crystalline layer 22 (e.g., nickel or cobalt).

Through experimentation, it was discovered that an outer nano-crystalline layer 22 that included cobalt or cobalt alloy began to discolor after exposure to aqueous corrosive environments (e.g., salt spray) simulating an accelerated environment in which an aerospace component may be exposed to harsh conditions. Through additional testing, it was determined that the discoloration appeared to be only topical and had little to no impact on the mechanical, strength, and corrosion-resistant properties of the coating system and underlying article over long term exposure. However, the discoloration generated secondary consequences including a poor aesthetic appearance and an impression of reduced reliability/integrity of the article which impacted the viability of the article for use in operation.

While not wanting to be bound to a specific scientific theory, the discoloration of the cobalt-based nano-crystalline layer 22 is believed to be caused by the partial oxidation of the top surface of the cobalt-based coating, attributable to the exposure of the layer to the aqueous environment which led to several complex chemical interactions and ultimately caused the cobalt metal of the nano-crystalline layer 22 to oxidize, thereby giving the article a red or rusty appearance. The oxide formed is considered to be a passive component that affected only the top surface of the coating. Through additional experimentation, it was surprisingly found that applying an outer corrosion resistant layer 24 to a cobalt-based nano-crystalline layer 22 reduced or substantially prevented the discoloration of nano-crystalline layer 22.

Corrosion resistant layer 24 may include materials suitable for reducing or substantially preventing corrosion staining. Examples of suitable materials may include, for example, coarse-grain nickel metal or nickel metal alloys such as nickel-phosphorus alloy (e.g., electroless nickel with about 1-13 weight percent (wt. %) phosphorus), nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy; tin (stannum) metal or tin metal alloys such as tin-zinc alloy; zinc metal; cadmium metal; and chromium metal. Corrosion resistant layer 24 may be applied to nano-crystalline layer 22 using any suitable process including, for example, electro-deposition, electroless deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), gas condensation, cold spraying, thermal spraying, blast spraying, or the like. In some examples, the resultant thickness of corrosion resistant layer 24 may be about 0.001 inches (e.g., about 0.025 mm).

In some examples, corrosion resistant layer 24 may corrode to form of a passive layer that does not undergo discoloration. In some examples, the formation of the corroded passive layer may inhibit corrosion or discoloration of nano-crystalline layer 22.

In some examples, nano-crystalline layer 22 may be deposited as a plurality of nano-crystalline layers or a plurality of underlying layers that includes one or more nano-crystalline layers 22. In some such examples, the nano-crystalline layers deposited on article 10 may include different compositions of ultra-fine grain metals configured to impart different mechanical or physical properties to article 10. For example, FIG. 2 illustrates an example portion of an article 30 that includes a multilayer coating 32. Aside from the differences described herein, article 30 may be substantially the same as article 10 including substrate 12 and configured for use in aerospace applications. Multilayer coating 32 may include an optional metal base layer 34, a first nano-crystalline layer 36, a second nano-crystalline layer 38, and corrosion resistant layer 24. Optional metal base layer 34 may include a layer of metal or metal alloy that acts as a seed layer to promote the growth and adhesion of the subsequent electro-deposition of nano-crystalline layers 36, 38 on substrate 12.

In some examples, nano-crystalline layers 36, 38 each may be individually tailored to modify one or more structural, mechanical, physical, chemical (e.g., corrosion resistance), or thermal-resistivity properties of article 30. For example, first nano-crystalline layer 36 may include one or more metal or metal alloys configured to enhance the strength or durability of article 30. In some examples, first nano-crystalline layer 36 may include nickel metal or nickel alloy. A nickel based nano-crystalline layer may allow for increased tensile strength and hardness of the layer thereby contributing to the overall durability of article 30 while allowing for the layer to remain relatively thin (e.g., between about 0.05 mm to about 0.7 mm). The improved strength and hardness may improve impact damage resistance of article 30 against foreign objects, without substantially increasing the weight or production cost of article 30 compared to other traditionally impact resistant aerospace coatings and/or components, which have traditionally been formed or coated with high strength metals such as steel and titanium. Additionally, or alternatively, the improved strength associated first nano-crystalline layer 36 may permit the incorporation of lighter or less durable materials into substrate 12 without reducing the structural performance of article 30.

In some examples, second nano-crystalline layer 38 may form the outermost nano-crystalline layer (e.g., the nano-crystalline layer furthest from substrate 12) and may include cobalt metal or a cobalt alloy to impart corrosion resistant characteristics to article 30 and any underlying layers (e.g., substrate 12, base layer 34, and first nano-crystalline layer 36). The relative thicknesses of first and second nano-crystalline layers 36 and 38 may be substantially the same (e.g., the same or nearly the same) or may be different depending on the composition of the respective layer and intended application of article 30.

In some examples, articles 10 and 30 may be in the form of an aerospace component that may benefit from one or more of the described strength, corrosion resistance, and reduced weight characteristic described above. In some examples, articles 10 and 30 may include aerospace components including, for example, cold section turbine engine components such as fan modules, fan blades, and the like; supports; struts; compressor section components such as vanes, blades, casings, and the like; engine inlet components; bypass components; housings members; brackets; ducts; nose cones; airfoils (e.g., blades or vanes); flaps; casing; panels; tanks; covers; air flow surfaces; particle separators; and the like. In some examples, articles 10 and 30 and/or substrate 12 may exhibit complex three-dimensional geometries such as turbine blade or vane. In other examples, articles 10 and 30 may be in the form of a sheet or a shaped-sheet component used such as an air flow surface, or housing component.

FIG. 3 is a flow diagram illustrating an example technique for forming an example article 30 that includes a multi-layer 32 coating on substrate 12. While the techniques of FIG. 3 are described with concurrent reference to the schematic diagram of FIG. 2, in other examples, the techniques of FIG. 3 may be used to form other articles and aerospace components, the articles and components of FIGS. 1-2 may be formed using a technique different than that described in FIG. 3, or both.

The technique of FIG. 3 includes depositing an optional base metal layer 34 on a substrate 12 (40), depositing at least one nano-crystalline layer 36, 38 on a substrate at least a portion of substrate 12 (42), and depositing a corrosion resistant layer 24 on the at least one nano-crystalline layer 36, 38 (44).

As described above, substrate 12 may include any suitable material. In some examples, substrate 12 may be formed from relatively light weight materials including for example, polymeric materials such as PEEK, PA, or the like; reinforced polymeric materials; light weight metals; ceramic materials (e.g., SiC based ceramics); or the like. In some examples, substrate 12 may include a porous structure such as a foam material (e.g., metal-based foam substrate), a lattice structure, a truss structure, or similar complex three-dimensional structure that includes a plurality of pores. In some such examples, the porous structure may be initially coated with a polymer of metal prior to the application on the one or more nano-crystalline layers 36, 38. Substrate 12 may be formed using any suitable technique, which may depend on the type of material used to form substrate 12. In some examples, substrate 12 may have a complex three-dimensional geometry.

The technique of FIG. 3 includes optionally depositing a base metal layer 34 on substrate 12 (40). The decision to deposit base metal layer 34 on substrate 12 may be dependent in part on the choice of materials of substrate 12. For example, in situations where substrate 12 includes one or more polymer based materials (e.g., non-conductive materials), the application of base metal layer 34 may help facilitate the deposition and adhesion of nano-crystalline layer 36 to substrate 12 during an electro-deposition process. Base metal layer 34 may include any suitable metal or metal alloy and may be deposited using any suitable technique including for example, electroless deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), cold spraying, gas condensation, or the like.

The technique of FIG. 3 also includes depositing at least one nano-crystalline layer 36, 38 on at least a portion of the substrate 12 (42). As described above, nano-crystalline layers 36, 38 may include layers of nano-crystalline metal (e.g., nickel, cobalt, copper, iron, or the like) or metal alloy (e.g., nickel-based alloy, cobalt-based alloy, copper-based alloy, iron-based alloy, or the like) that define an ultra-fine-grain microstructure with an average grain size less than about 50 nm, less than about 20 nm, or less than about 5 nm. The metallic nano-crystalline layer 36, 38 may be applied using an electro-deposition process (e.g., pulse electro-deposition using an electrolyte bath).

Depending on the type of application for article 30, the nano-crystalline layer may be deposited (42) as two or more metallic nano-crystalline layers 36, 38 with different metallic compositions each tailored to serve a different purpose. For example, first nano-crystalline layer 34 may include primarily nano-crystalline nickel metal or nickel alloy for improved strength and impact resistance, and a second nano-crystalline layer 38 may include primarily nano-crystalline cobalt or cobalt alloy for improved corrosion resistance.

In some examples, the at least one nano-crystalline layer (e.g., nano-crystalline layer 38) formed on substrate 12 (42) may include cobalt metal or cobalt alloy (e.g., cobalt-nickel alloy) to provide corrosion resistance to substrate 12.

The technique of FIG. 3 also includes depositing a corrosion resistant layer 24 (42) on the at least one nano-crystalline layer (e.g., nano-crystalline layer 38). In some examples, corrosion resistant layer 24 may help prevent or inhibit (e.g., slow) the corrosion, degradation, and/or reactions associated with moisture, oxygen, or other deleterious aqueous corrosion elements, thereby reducing the corrosion and degradation of nano-crystalline layer 36, 38. In examples where the at least one nano-crystalline layer 36, 38 includes cobalt metal or cobalt alloy (e.g., cobalt-nickel alloy), the deposition of corrosion resistant layer 24 has been found to prevent or inhibit the discoloration of the underlying layers. In some examples, corrosion resistant layer 24 may include, for example, nickel metal or nickel metal alloys such as nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy; tin (stannum) metal or tin metal alloys such as tin-zinc alloy; zinc metal; cadmium metal; and chromium metal. Corrosion resistant layer 24 may be applied to nano-crystalline layer 38 using any suitable process including, for example, electro-deposition, electroless deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), gas condensation, cold spraying, thermal spraying, blast spraying, or the like.

In some examples, corrosion resistant layer 24 may inhibit the discoloration of multi-layered coating 14 during a salt spray corrosion test (e.g., ASTM B117) compared to a nano-crystalline layer including cobalt or cobalt alloy that excludes the presence of outer corrosion resistant layer 24. The salt spray corrosion test may be carried out at about 35° C. over about a 24 hour period.

EXAMPLES Comparative Example 1

Three articles were prepared and coated with a nano-crystalline layer. The articles included a single nano-crystalline layer composed of a cobalt-nickel alloy. The three coated articles were subjected to a salt spray corrosion test in accordance with ASTM B117. In particular, the articles were placed in a salt spray chamber maintained at 35±2° C. A salt solution was prepared by dissolving approximately 5±1 parts by mass of sodium chloride in 95 parts of water and sprayed onto the articles using a spray atomizer for approximately 24 hours before taken out for initial observation (FIG. 4A) followed by continued exposure for approximately 200 hours in total (FIG. 4B). As shown in FIGS. 4A and 4B, the three articles experienced significant discoloration, having a dark red-brown appearance.

Example 1

An article was prepared and coated with a single nano-crystalline layer composed of a cobalt-nickel alloy as described in Comparative Example 1. The article was subsequently coated with a nickel-phosphorus alloy corrosion resistant layer over the nano-crystalline layer. The corrosion resistant layer was applied using electroless deposition to result in a corrosion resistant layer having a coating thickness of about 0.025 mm.

The coated article of Example 1 was subjected to the same ASTM B117 salt spray corrosion test decided above. After approximately 48 hours of exposure to the salt spray solution, the article was removed from the salt spray chamber and observed. As shown in FIG. 5, the article coated with the additional corrosion resistant layer exhibited minimal discoloration and maintained a generally grey metal finish.

Various examples have been described. These and other examples are within the scope of the following claims. 

What is claimed is:
 1. An article comprising: a substrate; and a multi-layered coating on at least a portion of the substrate, the multi-layered coating comprising: at least one nano-crystalline layer comprising a metal or a metal alloy, the nano-crystalline layer defining an average grain size of less than 50 nanometers (nm), and a corrosion resistant layer on the at least one nano-crystalline layer, wherein the corrosion resistant layer comprises at least one of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.
 2. The article of claim 1, wherein the corrosion resistant layer is configured to inhibit the discoloration of the multi-layered coating during a salt spray corrosion test at about 35° C. over about a 24 hour period.
 3. The article of claim 1, wherein the corrosion resistant layer comprises nickel metal or an alloy of nickel.
 4. The article of claim 1, wherein the substrate comprises a polymeric material.
 5. The article of claim 4, wherein the substrate further comprises reinforcement fibers.
 6. The article of claim 4, wherein the polymeric material comprises at least one of polyether ether ketone (PEEK), polyamide (PA), polyimide (PI), bis-maleimide (BMI), epoxy, phenolic polymers (e.g., polystyrene), polyesters, polyurethanes, silicone rubbers, and combinations thereof.
 7. The article of claim 1, wherein the at least one nano-crystalline layer comprises cobalt or cobalt alloy.
 8. The article of claim 7, wherein the at least one nano-crystalline layer comprises cobalt-nickel alloy.
 9. The article of claim 1, wherein the at least one nano-crystalline layer comprises a first nano-crystalline layer comprising a first metal or metal alloy and a second nano-crystalline layer comprising a cobalt or cobalt alloy, wherein the second nano-crystalline layer is in direct contact with the corrosion resistant layer.
 10. The article of claim 1, wherein the article comprises a component for a gas turbine engine selected from a group consisting of a cold section component, an engine inlet component, a particle separator, a support structure, a bracket, a blade, a vane, or an engine casing.
 11. The article of claim 1, wherein the corrosion resistant layer comprises nickel-phosphorus alloy.
 12. The article of claim 1, wherein the corrosion resistant layer comprises a coarse-grain metal or metal alloy.
 13. A method of forming an article comprising: depositing at least one nano-crystalline layer on a substrate, the at least one nano-crystalline layer comprising a metal or a metal alloy and defines an average grain size of less than 50 nanometers (nm); and depositing a corrosion resistant layer on the at least one nano-crystalline layer, wherein the corrosion resistant layer comprises at least one of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy.
 14. The method of claim 13, wherein the corrosion resistant layer is configured to inhibit the discoloration of the multi-layered coating during a salt spray corrosion test at about 35° C. over about a 24 hour period.
 15. The method of claim 13, wherein the corrosion resistant layer comprises nickel metal or an alloy of nickel.
 16. The method of claim 13, wherein the nano-crystalline layer comprises cobalt or cobalt alloy.
 17. The method of claim 13, wherein depositing the corrosion resistant layer comprises depositing by electroless deposition a coarse-grain nickel-phosphorus alloy.
 18. The method of claim 13, further comprising depositing a base metal layer on the substrate, wherein the base metal layer is between the substrate and the at least one nano-crystalline layer.
 19. The method of claim 13, wherein the substrate comprises a polymer.
 20. An article comprising: a substrate; and a multi-layered coating applied on at least a portion of the substrate, the multi-layered coating comprising: a first nano-crystalline layer comprising a metal or a metal alloy, the first nano-crystalline layer defining an average grain size of less than 50 nanometers (nm), and a second nano-crystalline layer on the first nano-crystalline layer, the second nano-crystalline layer comprising cobalt or cobalt alloy, the second nano-crystalline layer defining an average grain size of less than 50 nm, and a corrosion resistant layer deposited on the second nano-crystalline layer, wherein the corrosion resistant layer comprises a component selected from the list consisting of nickel metal, tin metal, zinc metal, cadmium metal, chromium metal, nickel-phosphorus alloy, nickel-sulfur alloy, nickel-boron alloy, nickel-cadmium alloy, nickel-zinc alloy, and tin-zinc alloy. 